1. Field of the Invention
This invention relates to articles and methods for applying temperature indicating compositions to heat recoverable articles.
2. Introduction to the Invention
Temperature indicating compositions are typically compositions which change color on being heated to a typical, usually well-defined, temperature. The change in color is frequently reversible and associated with a reversible chemical change which occurs at that temperature. Such materials are discussed and reviewed, for example, in two articles by Jesse H. Day in Chem. Rev. 63, 65 (1963) and Chem. Rev. 68, 649 (1968).
Typically temperature indicating compositions are used as warning indicators that a certain maximum safety temperature has been reached or as means whereby a subsequent check will reveal that some critical temperature was attained.
One especially interesting application of temperature indicating compositions has been in the field of heat-recoverable articles. Heat recoverable articles include heat-shrinkable polymeric sleeve described and claimed, for example, in U.S. Pat. Nos. 2,027,962; 3,086,242; 3,597,372; 3,379,218 and British Pat Nos. 1,155,470; 1,211,988 and 1,346,479, and also heat-recoverable articles based on fabrics as described for example in European Patent Publication Nos. 0116393; 0117026, and 0116392. These comprise a recoverable fabric in conjunction with a polymeric matrix formed by laminating a polymeric material to one or both sides of the fabric to render it impervious. Another type of heat-recoverable article is described in British Patent No. 1,440,524 in which an elastomer member such as an outer tubular member is "held out" in a stretched state by a second member, such as an inner tubular member, which upon heating weakens and thus allows the elastomeric member to recover.
These heat-recoverable articles are typically provided with a sealant coating, for example on the inner surface of a heat-shrinkable sleeve, so that a seal is made between the sleeve and a substrate such as a pipe or cable when the sleeve shrinks around it. The sealants are usually mastics or hot-melt adhesives. In such cases, heat is required both to shrink the sleeve and to melt the sealant. The heating may be by an externally applied torch or may be electrically applied, e.g. by forming the sleeve of a conductive polymeric material, or by laminating electrical wires in the Sleeve, as described for example in European Patent Publication No. 158519 (B100COM EPC). Whichever heating means is used it is desirable to ensure that the sleeve does not become too hot to deteriorate it, and yet, on the other hand, it is important that sufficient heat is applied to cause the sealant to melt and flow when in contact with the substrate. It has been proposed therefore in, for example, U.S. Pat. No. 3,816,335; British Pat. No. 1,511,053 and U.S. Pat. No. 4,344,909, to use a suitable temperature indicating composition on the surface of the heat-recoverable article in order to monitor and control the heat during recovery.
Known temperature indicating compositions are typically applied using a solvent. U.S. Pat. No. 4,344,909, for example, describes a temperature indicating composition comprising an organic thermochromic material, e.g. allantoin, a polymeric binder, e.g. an acrylic resin, and an organic solvent, preferably a halogenated, e.g. chlorinated, solvent such as 1,1,1-trichloroethylene and mixtures thereof.